1. Field of the Invention
The present invention relates to projection systems employing a single light valve.
2. Description of the Related Art
Light valves operating in a transmission or reflection mode, using liquid crystal, moving mirror, oil film, or other technologies are known for modulating a cross section of a light beam in two dimensions in response to an image control signal. A key use of such light valves is in systems employing rear or front projection of light to display video images, in particular color video images. Prior art single lamp, single light valve systems provide full color through a variety of methods, such as employing red, green and blue sub-pixels in the light valve with microfilters, color sequential addressing or falling raster addressing. The choice of lamps suitable for light valve projection is very limited, especially if long life is desired. One suitable lamp from the point of view of long life and high lumens per watt is the 100 W UHP lamp available from Philips Lighting, or similar lamps available from other manufacturers. The main problem with using these long life, short arc lamps is that, they often cannot be scaled up to higher power levels. In general, higher power lamps such as xenon or metal halide have other undesirable properties such as short life or large arc size. Therefore, if a brighter system is desired, multiple lamps must be used.
A two lamp, one light valve system is disclosed in commonly-owned U.S. Pat. No. 5,386,250. This patent describes a two lamp projection system where a deformable micro-mirrored device (DMD) is used as a combiner of the lamp outputs. This system suffers from two main problems: high cost and low efficiency of the DMD, such that even with improvements in efficiency expected in the near future, there would be far less than a doubling of brightness of the light illuminating the light valve relative to illumination from a single lamp.